The longest homogeneous series of grape harvest dates, Beaune 1354–2018, and its significance for the understanding of past and present climate

Abstract. Records of grape harvest dates (GHD) are the oldest and the longest continuous phenological data in Europe. However, many available series including the well-known (Dijon) Burgundy series are error prone, because scholars so far uncritically drew the data from nineteenth century publications instead of going back to the archives. The GHD from the famous vine region of Beaune (Burgundy) were entirely drawn from the archives, critically cross checked with narrative evidence and calibrated with the long Paris temperature series comprising the 360 years from 1659 to 2018. The 664-year-long Beaune series from 1354 to 2018 is also significantly correlated with tree-ring and documentary proxy evidence as well as with the Central European temperature series (from 1500). The series is clearly subdivided into two parts. From 1354 to 1987 grapes were on average picked from 28 September on, whereby during the last 31 year long period of rapid Global Warming from 1988 to 2018 harvests began 13 days earlier. In the Paris temperature measurements since 1659, April-to-July temperature reached the highest value ever in 2018. The 33 extremely warm events comprising the 5 % percentile bracket of GHD are unevenly distributed over time. 21 of them occurred between 1393 and 1719, whereby this is the case for just five years between 1720 and 2002. Since the hot summer 2003 8 out of 16 spring-summer periods were outstanding according the statistic of the last 664 years, no less than 5 among them within the last 8 years. In sum, the 664-year-long Beaune GHD series demonstrates that outstanding hot and dry years in the past were outliers, whereby they became the norm since the transition to rapid Global Warming in 1988.